Simulation studies of R2(Δη,Δφ) and P2(Δη,Δφ) correlation functions in pp collisions with the PYTHIA and HERWIG models

Abstract

We report studies of charge-independent (CI) and charge-dependent (CD) two-particle differential-number correlation functions, $\rm{R_{2}}(\Delta\eta, \Delta\varphi)$, and transverse momentum ($p_{\rm T}$) correlation functions, $\rm{P_{2}}(\Delta\eta, \Delta\varphi)$, of charged particles in $\sqrt{\textit{s}}$ = 2.76 TeV pp collisions with the PYTHIA and HERWIG models. Model predictions are presented for inclusive charged hadrons ($h^\pm$), as well as pions ($\pi^\pm$), kaons (K$^\pm$), and (anti-)protons ($\rm \bar{p}$/p) in the ranges $0.2 < \textit{p}_{\rm T} \le 2.0~\rm{GeV}/\textit{c}$, $2.0 < \textit{p}_{\rm T} \le 5.0~\rm{GeV}/\textit{c}$, and $5.0 < \textit{p}_{\rm T} \le 30.0~\rm{GeV}/\textit{c}$, with full azimuthal coverage in the range $|\eta|< 1.0$. We compare the model predictions for the strength and shape of the $\rm{R_{2}}$ and $\rm{P_{2}}$ correlators as these pertain to recent measurements by the ALICE collaboration. The $\rm{R_{2}}$ and $\rm{P_{2}}$ correlation functions estimated with PYTHIA and HERWIG exhibit qualitatively similar near-side and away-side correlation structures but feature important differences. Our analysis indicates that comparative studies of $\rm{R_{2}}$ and $\rm{P_{2}}$ correlation functions would provide valuable insight towards the understanding of particle production in pp collisions, and by extension, should also be useful in studies of heavy-ion collisions. Comparison of the $\Delta \eta$ dependence of $\rm{R_{2}}$ and $\rm{P_{2}}$ could contribute, in particular, to a better understanding and modeling of the angular ordering of particles produced by hadronization in jets, as well as a better description of jet fragmentation functions of identified species at low momentum fraction $(z)$.